Polymer-based nano-composites offer unique properties. These nano-composites are made by adding particles to a polymer matrix to get a nano-composite having properties of both the particles and the polymer matrix. This can result in a synergistic effect, thereby enhancing the properties of the matrix. Important properties include electrical conductivity, thermal conductivity, and dielectric permittivity.
Some nano-composites require high particle loading to reach the required percolation of particles necessary to achieve the desired properties. In one example, more than 50 volume % of dielectric particles was needed to increase the dielectric constant of polymer composites to a sufficient level. There, the thermal conductivity of SiC/epoxy composites was found to be less than 3.9 W*(m*K) when the particle loading was 50%. When high particle loading is utilized, certain properties of the polymers are reduced, such as flexibility, transparency, and processability.
For nano-composite films used in electronic applications, it is generally necessary to use films having enhanced properties in a certain direction. One of the methods to achieve the improvement of properties in a direction that does not require high particle loading is aligning the particles in an electric field. The alignment of electrical or thermally conductive particles can form an electrical or thermal conductive path way. For example, the alignment of lead zirconate titanate (PZT) nanowires in polyvinylidene fluoride (PVDF) in the Z direction can achieve much higher dielectric constant than similar composites with randomly aligned nanowires due to the increased particle-particle interactions after alignment.
Thermal or UV-curable resins are the most commonly used polymer matrix materials for nano-composite films, because of the ease of use in continuous processes. The particles can form chains under an electric field, and then the chain-like particle structures are frozen or cured in the matrix materials by thermal heat or UV light. However, there are disadvantages to using thermal or UV-curable resins such as having a high viscosity such that the particles are unable to move to achieve alignment. Also, the suitable materials are limited to thermoset materials. Where polymer solutions having solvents have been utilized, in-plane alignment has proven difficult for continuous production due to the evaporation of the solvents causing the resulting film to decrease in thickness. This leads to an alteration of the directed alignment of the nanostructure columns. Thus, a need remains for the continuous production of nano-composite films having vertically aligned particles and a smooth top surface